Savannah monitor hatchling

Question
Hello, I'm reaching out to you because I recently rescued a savannah hatching from a Petco that was a return because it was 'aggressive'... I'm in the middle of building him a large enclosure but at the moment He is in a 20 gal tank. 1/3 of the tank is a mineral sand with a piece of slate with for basking. The surface temp on the basking spot is 120-130 degrees while the cooler side of the tank is ground coconut husk deep enough for a nice area to dig with a hideout and stays between 80-95 during the day. The humidity is good and has a nice big water dish to hangout in. He seemed pretty lethargic since I've had him about a week now. I got him to eat the first two days with no trouble at all. But now all he want to do is sleep. He won't pay any attention to the food. I have raised a savannah monitor before and had him for 8 years, never had an issue especially when it comes to feeding. Do you have any ideas on getting him to eat. Like I said he's a hatching so he has been on a diet of mainly crickets and mealworms with every other feeding being coated in vitamins. Thank you for taking the time to read this, fIsh look forward to your response.

Answer
Your efforts should be applauded.  However, remember that reptiles have a Type III survivorship curve-meaning the vast majority of them die early in life.  SO you could do everything right and it still might not make it.  I don't love sand for ANY small reptiles as, if ingested it can cause impaction.  Indoor/outdoor carpet or newspaper makes a good albeit not as attractive replacement.  You could try checking his stool for parasites, but honestly it's probably too late if he's stopped eating.  Try soaking him in Pedialyte, sometimes that perks them up.